Compact biometric authentication device and associated methodology of imaging and detecting living-tissue patterns

ABSTRACT

The present invention enables permanent biometric authentication without the risk of forgery or the like. The present invention enables living-tissue discrimination as well as biometric authentication. The roughness distribution pattern of deep-layer tissue of the skin covered with epidermal tissue is detected, thereby extracting a unique pattern of the living tissue. Then, biometric authentication is performed based upon the detected pattern. The roughness distribution pattern of the deep-layer tissue of the skin is optically detected using difference in optical properties between the epidermal tissue and the deep-layer tissue of the skin. In this case, long-wavelength light, e.g., near-infrared light is used as illumination light cast onto the skin tissue. A fork structure of a subcutaneous blood vessel is used as the portion which is to be detected, for example. The portion which is to be detected is determined based upon the structure of the fork structure. In this case, the living-tissue discrimination may be made using the subcutaneous blood vessel.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/015,263 filed Jan. 16, 2008, which is a continuation of U.S.application Ser. No. 10/512,087 filed on Apr. 7, 2005, which is aNational Stage of PCT/JP03/05696, filed on May 7, 2003, all of whichclaim priority to Japanese Patent Application No. 2002-134569, filed May9, 2002 and Japanese Patent Application No. 2002-134534, filed May 9,2002. The contents of each of these documents are incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to a new biometric pattern detectingmethod and biometric pattern detecting device for acquiring the patternof a deep skin layer such as dermis or the like, and particularly to abiometric authentication method and a biometric authentication device.

BACKGROUND ART

Fingerprints, palm patterns, or the like, are widely used for personauthentication. These patterns are skin ridge patterns wherein a part ofthe epidermal tissue is embedded in the roughness structure of thedermis, and accordingly, the patterns can be directly observed from theoutside. That is to say, the aforementioned pattern essentiallycorresponds to the deep layer structure of the skin such as dermis orthe like. The skin of the portion such as a palm, a sole, or the like,has a special structure wherein the epidermal structure corresponds tothe structure of the dermis beneath the epidermal tissue, unlike theskin of other portions, leading to the physiological advantages such ashigh sensitivity of the touch sensory nerves of which ends arepositioned in the deep layer of the skin to external stimulation, greattoughness regarding friction, and so forth. Conventionally, thefingerprints have been used for person authentication since thefingerprints exhibit sufficient stability essentially due to the highstability of the deep layer structure therebeneath.

However, the aforementioned biometric authentication using thefingerprints does not provide sufficient security against so-called“spoofing” or the like. That is to say, the fingerprints are readilyleft on various objects, and the fingerprints left on the object can beeasily observed, leading to a risk that other persons would forge thefingerprints.

On the other hand, it is expected that biometric authentication usingthe epidermal tissue of other portions avoids the aforementioned risk offorgery, for example. However, the epidermal tissue changes due tometabolism thereof in a 28-day cycle. Furthermore, the epidermal tissuereadily exhibits various conditions due to rough skin, dry skin, or thelike. Accordingly, the epidermal tissue of other portions does not havesufficient stability. Furthermore, it has become clear from measurementthat the patterns of the epidermal tissue of the base portion of afinger, the thenar region, and the like, do not correspond to thepatterns thereunderneath at all, rather, in some cases, the patterns ofthe epidermal tissue thereof are formed orthogonal to the patternsthereunderneath, except for a special case such as the fingerprints,leading to difficulty in biometric authentication using such a portion.

That is to say, a large part of the epidermal tissue of the human body,including the palm portion such as the thenar region and so forth, thebase portion of a finger, the skin of the back of the hand, and thelike, has patterns different from the patterns of the deep-layerstructure therebeneath, except for a special case such as thefingerprints which are fingertip impressions, wherein the epidermaltissue directly corresponds to the deep-layer structure, allowingexternal observation thereof. Furthermore, it is difficult to makeexternal observation of the deep-layer structure therebeneath due toscattering of visible light from the 6-layer epithelial structure andabsorption thereof by the melanin pigment in basal cells or the like.This leads to difficulty in development of a finger-ring-typeauthentication device wherein person authentication is performed usingthe pattern of the skin in contact with the inner face of the fingerring at the time of being fit by the user.

On the other hand, the deep-layer structure beneath the epidermal tissueis essentially unique to an individual, and exhibits sufficientstability over time, as with a well-known example of fingerprints or thelike. Note that a tattoo wherein a pigment is injected into thedeep-layer structure, and a stretch mark caused by pregnancy, also havethe same stability due to the properties of the deep-layer structurebeneath the epithelium tissue. Accordingly, it is expected that thepattern beneath the epithelium tissue, i.e., the deep-layer structure ofthe epithelium tissue is suitably used for biometric authentication.However, the aforementioned patterns cannot be directly observed,neither left on an object by contact with the object, and accordingly,development of the authentication device using the pattern of thedeep-layer structure has not been made, although the pattern of thedeep-layer structure has the same performance of biometricauthentication as with fingerprints.

The present invention has been made in order to solve the aforementionedproblems, and accordingly, it is an object thereof to provide abiometric pattern detecting method and biometric pattern detectingdevice for acquiring the roughness structure distribution of thedeep-layer structure beneath the epithelium tissue (patterns beneath theepithelium tissue) or the blood-vessel pattern beneath the epitheliumtissue, which cannot be directly observed. Furthermore, it is an objectof the present invention to provide a biometric authentication methodand a biometric authentication device which enables stable biometricauthentication while preventing a risk of “spoofing”, e.g., forgery orthe like.

DISCLOSURE OF INVENTION

The present inventor has made various studies in order to achieve theaforementioned object. As a result, it has become clear thatdiscrimination can be made between epidermal tissue and deep-layertissue of the skin using difference in properties (optical properties,electric properties, and temperature difference) therebetween, and theroughness distribution pattern of the deep-layer tissue of the skinwherein visual observation is difficult due to shielding with epidermisis clearly detected. Accordingly, it has become clear that the patternof any desired portion of the skin and subcutaneous tissue over theentire body of the user can be detected, as well as a special portionwhere the epidermal pattern corresponds to the dermal pattern such asfingerprints or the like, and the pattern thus detected can be appliedto biometric authentication (person authentication).

The present invention has been made based upon the information thusobtained. That is to say, with a living-tissue pattern detecting methodaccording to the present invention, the roughness distribution patternof the deep-layer tissue of the skin covered with the epidermal tissueis detected using difference in properties (optical properties, electricproperties, and temperature difference) therebetween, thereby extractinga unique pattern of the living tissue. Furthermore, a living-tissuepattern detecting device according to the present invention includesmeans for detecting the roughness distribution pattern of the deep-layertissue of the skin covered with the epidermal tissue. Furthermore, witha biometric authentication method according to the present invention,the roughness distribution pattern of the deep-layer tissue of the skincovered with the epidermal tissue is detected so as to be compared to apattern registered beforehand, whereby biometric authentication isperformed. Furthermore, a biometric authentication device according tothe present invention includes means for detecting the roughnessdistribution pattern of the deep-layer tissue of the skin covered withthe epidermal tissue, and the pattern thus detected is compared to apattern registered beforehand, whereby biometric authentication isperformed.

The present invention has been made based upon the basic concept thatauthentication is performed not using an epidermal pattern, but usingthe pattern of the deep-layer tissue of the skin, e.g., a dermalpattern. The roughness distribution pattern (pattern) of the deep-layertissue is unique to individual living tissue as with fingerprints, palmpattern, sole pattern, and so forth, and exhibits small change overtime, i.e., exhibits high stability. Furthermore, the deep-layer tissueof a large part of the skin has a different pattern from that of theepidermal layer, except for special portions such as a fingertip havingfingerprints which can be observed from the outside, or the like.Furthermore, the pattern of the deep-layer tissue is covered with theepidermal tissue, leading to difficulty in visual observation from theoutside. Furthermore, no impression is left on any object even if thetissue comes in contact with the object. Accordingly, it is almostimpossible for other persons to forge such a pattern.

Furthermore, with the present invention, the system does not detect thestructure of dead tissue having no nucleus such as the horny layer ofthe skin, specifically, fingerprints, and so forth, but detectsdeep-layer tissue of the skin which is living tissue, as describedabove. The deep-layer tissue of the skin does not maintain the patternthereof if the deep-layer tissue is cut off from the living human body.For example, the deep-layer tissue of the skin has blood capillariestherein, and the pattern formed of the blood flow within the bloodcapillaries is unique to the living tissue. Furthermore, if the tissueis cut off from the living human body, the aforementioned pattern isimmediately lost due to contraction of blood vessels, retention ofblood, lost of blood, and so forth. This affects the pattern of theentire deep-layer tissue of the skin. Thus, with the present invention,the biometric authentication and the living-tissue discrimination areintegrated, thereby suppressing the risk of “spoofing” using the tissueof the user to an unrealistic level, and thereby realizing true“biometric authentication”.

The aforementioned deep-layer tissue of the skin, e.g., the roughnessdistribution pattern of dermal layer can be optically detected using thefact that difference in the structure between epidermal tissue formed ofsimple cells or dead cells thereof and dermal tissue which is denseconnective tissue causes difference in scattering properties andrefraction properties therebetween, and this leads to depolarization ordifference in frequency between the incident light and the returninglight.

Specifically, first, polarized light is cast onto the tissue, as well asdetecting the reflected light through a polarizing filter with thepolarizing plane orthogonal to that of the aforementioned polarizedlight, thereby detecting the aforementioned roughness distributionpattern. In this case, the polarized light is cast on the surface of thetissue, and the reflected light is filtered with the polarizing filterwith the polarizing plane orthogonal to the aforementioned polarizedlight, and accordingly, only the depolarized light due to scattering inthe living tissue, such as back-scattered light, light split due tobirefringence, and so forth, is detected, thereby extracting the patternof the tissue having the nature which causes scattering of light, suchas a dermal layer beneath epidermis and so forth. In particular, anarrangement may be made wherein long-wavelength light such asnear-infrared light and so forth, which has the nature that the lightreadily passes through the epidermal tissue, and is readily scattered indermal tissue, is employed as the aforementioned polarized light,thereby reducing adverse effects due to absorption of the polarizedlight in the living tissue, and thereby effectively detecting thepattern of the subcutaneous tissue beneath epidermis due to desirableoptical properties (scattering properties, birefringence properties, andso forth) of the subcutaneous tissue beneath epidermis.

Second, an arrangement may be made wherein the illumination light iscase onto the tissue, as well as causing interference between a part ofthe illumination light and the reflected light so as to detect change inwavelength components of the reflected light in the form of aninterference pattern, thereby extracting a unique pattern of the livingtissue. In this case, the system causes interference between thereflected or scattered light from the skin and the incident light splitby a half mirror or the like serving as reference light, therebydetecting change in wavelength components due to birefringence orscattering in the internal structure of the skin in the form of a beatpattern (interference pattern). Such a beat pattern has propertiesunique to an individual living tissue, thereby enabling authenticationusing the beat pattern.

Furthermore, with the biometric authentication method and the biometricauthentication device according to the present invention, an arrangementmay be made wherein the subcutaneous tissue structure covered withepidermal tissue is electrically detected using difference in electricproperties between the epidermal tissue and the deep-layer tissue of theskin, and the subcutaneous tissue structure thus detected is compared toa pattern registered beforehand, thereby enabling biometricauthentication. Furthermore, an arrangement may be made wherein thesubcutaneous tissue structure covered with epidermal tissue is detectedusing difference in temperature between the epidermal tissue and thedeep-layer tissue of the skin, and the subcutaneous tissue structurethus detected is compared to a pattern registered beforehand, therebyenabling biometric authentication.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram which shows skin tissue.

FIG. 2 is a schematic diagram which shows an example of a detectingdevice (authentication device) for acquiring an image of dermal tissueusing depolarization due to back-scattering of light.

FIG. 3 is a schematic diagram which shows an example of a detectingdevice (authentication device) for taking an image of scattering lightfrom the skin at a desired depth.

FIG. 4 is a schematic diagram for describing a mechanism ofbirefringence measurement with the optical heterodyne interferometry.

FIG. 5 is a schematic diagram which shows an example of a detectingdevice (authentication device) for detecting the tissue pattern beneathepidermis using the scattering property pattern obtained due tointerference of the light returning from the skin.

FIG. 6 is a schematic diagram which shows an example of a detectingdevice (authentication device) having a configuration wherein multiplebeat detecting devices are arrayed.

FIG. 7 is a schematic diagram which shows an example of a detectingdevice (authentication device) having a configuration wherein a movingmirror is provided to an illumination unit for casting light onto theskin.

FIG. 8 is a schematic diagram which shows an example of a detectingdevice (authentication device) having a function for determining aportion which is to be authenticated, based upon a vein pattern.

FIG. 9 is a property chart which shows absorption spectra of oxidizedhemoglobin and reduced hemoglobin.

FIG. 10 is a property chart which shows difference in transmissivitybetween hemoglobin and water in living tissue.

FIG. 11 is a schematic diagram which shows an example of a detectingdevice (authentication device) for performing pattern detection with thedifferential interference method using near-infrared light.

FIG. 12 is a schematic diagram which shows an example of a skin-surfaceelectric-potential detecting device.

FIG. 13 is another schematic diagram which shows an example of askin-surface electric-potential detecting device.

FIG. 14 is a schematic diagram which shows a subcutaneous-tissue patterndetecting device having a configuration wherein the multipleskin-surface electric-potential detecting devices are two-dimensionallyarrayed.

FIG. 15 is a waveform chart which shows an example of anelectric-potential waveform observed when walking.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Detailed description will be made below regarding a biometric patterndetecting method, a biometric pattern detecting device, a biometricauthentication method, and a biometric authentication device, accordingto the present invention with reference to the drawings.

For example, the biometric authentication using the fingerprints has arisk of forgery by other persons since the impressions (fingerprints)are readily left on another object, and can be easily observed. As acountermeasure, there is the need to perform living-tissuediscrimination for determining whether or not the detected fingerprintshave been acquired from the live tissue without unauthorized means. Thereason is that the biometric authentication using the fingerprints isessentially measurement wherein the tissue structure of the dead tissuehaving no nucleus such as the horny layer of the skin is optically orelectrically detected.

The security performance of the biometric authentication using theaforementioned fingerprints, the iris, or the like, does not only dependupon the detection precision, but also the aforementioned living-tissuediscrimination. For example, let us say that other persons can breachthe living-tissue discrimination at the time of the biometricauthentication using the fingerprints, as well as having obtained thetissue used for the biometric authentication. This allows the otherpersons to easily make “spoofing”, resulting in deterioration in thesecurity of the system to zero. Furthermore, the aforementioned“spoofing” using the tissue leads to a new additional risk of a serioushazard to the body and the life of the user, as well as the financialrisk in a case wherein the security of the conventional credit card isbreached. The aforementioned serious hazard to the body and the life ofthe user will be referred to as “surgical hazard” hereafter.

The biometric authentication needs to provide not only the sufficientlimitation security performance which has been proposed in theconventional authentication techniques, but also the sufficient securityperformance against the surgical hazard for securing the safety of theuser, which has been hardly proposed in the conventional techniques.

That is to say, the security performance of the biometric authenticationconsists of two kinds of the security performance. One securityperformance depends upon the precision of the “authentication” foridentifying whether or not that the tissue which is to be authenticatedmatches the tissue of the user. The other security performance dependsupon the precision of the “living-tissue discrimination” for determiningwhether or not the tissue used for authentication is live tissue, i.e.,for confirming that the tissue is not dead tissue cut off from the bodyof the user. The conventional biometric authentication techniques haveprovided only the precision and reliability of the former securityperformance. In this case, the “biometric authentication” used hereessentially means authentication without “living-tissue discrimination”,and accordingly, does not mean true biometric authentication.Accordingly, from the practical perspective, the conventional securitysystem having such a problem may lead to the additional hazard, i.e.,the surgical hazard.

With the simplest spoofing method without any particular technique andequipment, spoofing is made using the tissue such as a finger, arm,eyeball, or the like, which has been cut off from the body of the user.Such a simple method for breaching the biometric authentication securityleads to a new additional and serious hazard to the life and body of theuser, of which money cannot replace, even in a case of small financeloss. Accordingly, the conventional biometric authentication methodsusing the fingerprints, iris within the eyeball, or the like, remainaccessory means used with other main authentication means, or remainaccessory means in a limited form for unimportant matter, or the like.This leads to difficulty in wide use of the conventional biometricauthentication.

On the other hand, forgery of the fingerprints or the like can berelatively easily made. As a countermeasure against forgery of thefingerprints, electrostatic capacity or electrostatic induction ismeasured between the finger and the electrode so as to detect thedistance between the surface of the skin and the electrode, therebydetecting the pattern of the fingerprints, using the fact that thesurface of the skin serves as a conductive material due to moisture(water) containing salt from sweat or the like secreted from the livetissue. This is a kind of an example of the biometric authenticationwith the “living-tissue discrimination”. The reason is that theaforementioned measurement is impossible without moisture which is anelectrolyte containing salt from sweat or the like secreted from thelive tissue.

However, while the aforementioned detecting method requires moistureserving as an electrolyte on the surface of the object which is to beauthenticated, the aforementioned object does not need to be alive. Thatis to say, with the aforementioned detecting method, the “living-tissuediscrimination” is not performed for confirming that the object which isto be authenticated has not been cut off from the body of the user, forexample. Accordingly, with the aforementioned detecting method, it isdifficult to reject unauthorized means such as forgery of thefingerprints formed of a gel material having water retentivity, or thefinger which has been cut off from the body of the user and subjected tospraying with or soaking in a physiological salt solution.

Furthermore, with the biometric authentication using DNA or the like,while forgery of the DNA is difficult, it is essentially impossible todiscriminate whether the DNA sample which is to be authenticated belongsto the live body of the user or is formed of DNA mass-produced byreplicating the DNA obtained from the dead body or a hair of the userwith the PCR (Polymerase Chain Reaction). Accordingly, the biometricauthentication using DNA does not include “living-tissuediscrimination”. Accordingly, the biometric authentication using DNAneeds some sort of a countermeasure such as a new separate sensor fordiscriminating whether or not the sample belongs to the live body of theuser with a suitable method such as detection of the blood flow in thefinger using infrared light and so forth, as well as “biometricauthentication”.

In this case, the “biometric authentication” is performed by two means.One is “authentication”, and the other is “living-tissuediscrimination”. That is to say, the conventional “biometricauthentication” does not only depend upon the “authentication” servingas a “front door” as if it were, but also “living-tissue discrimination”serving as a “back door” as if it were, which is performed in separatedetection means using a different physical principle. Accordingly, theconventional “biometric authentication” has a problem that if otherpersons breach the security of the “living-tissue discrimination”serving as a back door, the security of the biometric authenticationsecurity is breached, leading to a risk of “spoofing”, and furtherleading to a risk of surgical hazard. With the “living-tissuediscrimination”, the system discriminates whether the tissue which is tobe authenticated is alive or dead. However, the living tissue has greatdiversity, and accordingly, the “living-tissue discrimination” must beperformed for a single tissue sample with a sufficiently wide thresholdrange, as can be understood from the standing theory (central dogma)what life is. This leads to an essential problem of the poor security ofthe conventional “biometric authentication” against “spoofing”. That isto say, with the conventional “biometric authentication” having separatemeans formed of the means of “authentication” and the means of“living-tissue discrimination”, other persons can easily find andanalyze the discrimination mechanism for discriminating whether thetissue is alive or dead. Accordingly, there is demand for the “true”biometric authentication integrating the means of “authentication” andthe means of “living-tissue discrimination”, i.e., the biometricauthentication without the aforementioned “back door”.

With the present invention, biometric authentication is performed basedupon the detected roughness distribution pattern of the epithelialdeep-structure tissue, e.g., dermal layer, instead of patterns of theepidermal tissue such as fingerprints described above.

FIG. 1 is a schematic diagram which shows skin tissue which is roughlyclassified into epidermis 1 and dermis 2. The epidermis 1 is keratinizedstratified flattened epithelium formed of a horny layer 11, a lucidlayer 12, a granular layer 13, a prickle layer 14, a basal layer 15, anda basement membrane 16. Note that a layer formed of the granular layer13, the prickle layer 14, a basal layer 15, is referred to as“Malpighian layer”.

The horny layer 11 has a lamellar liquid crystal structure formed of abilayer membrane formed of a horny-layer intercellular lipid. The lucidlayer 12 has a cholesteric liquid crystal structure, and the granularlayer 13 is formed of cells of which cytoplasm contains basic structureswhich are referred to as “keratohyalin granule” having opticalproperties which cause reflection and scattering of light, like beads.On the other hand, the basal layer 15 has melanin granules. As describedabove, the skin tissue has a multi-layer structure having variousoptical scattering/absorption properties due to each layer, leading tothe advantage of preventing the living tissue from exposure toultraviolet light or the like. In particular, the epidermis 1 has a kindof dichroic properties for ultraviolet light due to the multi-layerstructure formed of thin membranes each of which has a differentrefractive index. However, the epidermis 1 is translucent tissue havingrelatively high scattering properties in a range of visible light,except for absorption of the light due to the melanin pigment. Note thatthe epidermis 1 has high transparency in a longer wavelength range thanwith red visible light or near-infrared light. Accordingly, the lightreflected from the blood flow in the blood capillaries within the dermis2 beneath the epidermis 1 is scattered. The scattered light is observedas a complexion or the color of the skin. Note that the color of theskin essentially depends upon the distribution of the melanin pigmentand the blood flow within the blood capillaries in the dermis 2. Theflow of an electrolyte fluid such as blood or lymph does not occur inthe epidermis 1, and accordingly, the epidermis 1 essentially serves asa dielectric as exemplified by the horny layer 11.

On the other hand, the dermis 2 has essentially different structure ascompared with the epidermis 1. The dermis 2 essentially comprises thedense fibrous connective tissue formed of collagen or elastin, and ablood capillary pattern, unlike the epidermis 1 formed of simple cellshaving no blood capillaries.

The dermis 2 is classified into a papillary layer and a reticular layer.The dermal papillary layer is in contact with the epidermal tissuethrough the basement membrane serving as the lowermost layer of theepidermal tissue, is formed of the connective tissue and the bloodcapillary pattern, and has the end of the sensory nerve. The reticularlayer is formed of collagen having an array structure, elastin forconnecting the collagen structures one to another, and a matrix whichfills the space therebetween. The dermis 2 contains a great amount ofthe electrolyte fluid due to great amount of blood capillaries and theflow of lymph or the like, leading to extremely high electricconductivity as compared with the epidermis 1.

[Method Using the Optical Properties]

While the collagen and elastic fibrous tissue forming connecting tissueof the dermis 2 exhibits high optical birefringence, the epidermaltissue does not exhibit birefringence. On the other hand, the epidermis1 has optical properties which cause scattering of light, andpolarization properties which cause depolarization of light due toscattering thereof. In a basic mechanism, the tissue exhibits a uniquevertical/horizontal polarization ratio dependent upon the size and shapeof the scattering particles therewithin.

In a case wherein the wavelength of the electromagnetic wave is fargreater than the particle size, Rayleigh scattering occurs.

In a case wherein the wavelength of electromagnetic wave generallymarches the particle size, Mie scattering occurs. (which causes thecolor of cloud particles, aerosol, and cumulonimbus, to appear white)

In a case wherein the wavelength of electromagnetic wave is far smallerthan the particle size, the electromagnetic wave geometrically passesthrough the object. (e.g., rainbow formed of rain particles, diamonddusts)

The dermis 2 having a thickness greater than a certain thickness appearswhite, like milk agar. Furthermore, the dermis 2 has optical propertieswherein the longer the wavelength of light is, the more readily thelight passes through the dermis 2. On the other hand, the shorter thewavelength of the light is, the more readily the light is scattered. Letus say that the dermis 2 contains a significant amount of absorptionpigment. In this case, the short-wavelength light scattered at a shallowportion returns to the eyes of the observer with a high probability.However, the long-wavelength light returns to the observer with a lowprobability due to absorption of the light in the pigment. Accordingly,the blood capillaries at the shallow portion of the skin appear vividred from external observation, and the vein and hemangioma positioned atrelatively deep portion appears relatively blue. Note that while thenevus (birthmark) due to melanocyte, which is positioned at the boundarybetween the dermis and the epidermis appears relatively brown from theexternal observation, the blue nevus positioned in the dermis appearsrelatively blue from the external observation, wherein the name agreeswith the color. Furthermore, the Ota's nevus and Mongolian spot due todermal melanocyte appear relatively blue from the clinical observation.

With the present invention, the system detects the roughnessdistribution pattern or the like of the deep structure of the skin(e.g., dermal tissue) using difference in optical properties or electricproperties between the dermal tissue and the epidermal tissue, wherebybiometric authentication is performed. For example, the reflected lightfrom the tissue sample is subjected to filtering so as to discriminatethe dermal layer formed of the connecting tissue, collagen fibroustissue, or the like, in a deeper portion, from the epidermal tissue,using the difference in the scattering/polarization properties of thereflected light as to the incident white light between the dermal tissueand the epidermal tissue. This enables the user to clearly discriminatethe dermal tissue wherein observation is difficult due to shading by theepidermal tissue, from the epidermal tissue. In particular, the presentinvention has the advantage of enabling person authentication bydetecting the pattern of the dermal tissue, even using the skin or thesubcutaneous tissue of any portion of the body of the use, as well as aspecial portion such as fingerprints and so forth, where the dermaltissue pattern matches the epidermal tissue pattern.

FIG. 2 shows a configuration example of a detecting device for acquiringan optical image of the dermis 2 beneath the epidermis having a greatdiversity of scattering mechanisms as described above. The detectingdevice has a configuration which allows the light returning due toscattering and birefringence to pass through the receiver of thedetecting device while preventing the light reflected from the epidermallayer from being received, by polarizing means including polarizingplates at the light-emitting unit and the light-receiving unit withplanes of polarization orthogonal one to another.

Description will be made below regarding a specific configuration.First, an illuminating optical system includes a light source 21,optical lens 22, and an illumination-unit polarizing plate 23. Anysuitable light source such as an LED or the like can be employed as thelight source 21. Note that a light source for emitting long-wavelengthlight such as near-infrared light or the like is preferably employed asthe light source 21 since such long-wavelength light has the nature toreadily pass through the epidermal tissue, as well as being reflected bythe dermal tissue. Such a configuration enables acquisition of thepattern of the tissue using the optical properties such as scatteringproperties, birefringence properties, and so forth.

On the other hand, an imaging optical system includes an imaging device(solid-state image sensor, e.g., CCD) 24 serving as a light-receivingdevice, an imaging lens set 25, and a receiving-unit polarizing plate26. Furthermore, a half mirror 27 is disposed on a light path betweenthe aforementioned illuminating optical system and the imaging opticalsystem. Note that the aforementioned illuminating optical system and theimaging optical system are disposed with the polarizing planesorthogonal one to another.

With the aforementioned detecting device, the illumination light is castfrom the light source 21 onto the skin with a single polarizing planedetermined by the illumination-unit polarizing plate 23. On the otherhand, the imaging optical system includes the receiving-unit polarizingplate 26 with the polarizing plane orthogonal to that of theillumination-unit polarizing plate 23. Accordingly, the reflected lightfrom the epidermal tissue through simple reflection passes through witha polarizing plane orthogonal to the polarizing plane of thereceiving-unit polarizing plate 26, whereby such reflected light isintercepted by the receiving-unit polarizing plate 26.

The illumination light cast onto the skin from the illumination opticalsystem reaches the deep-layer tissue of the skin (e.g., dermal tissue),leading to scattering of the light or birefringence thereof due tovarious kinds of tissue, resulting in depolarization thereof. Thereflected light, e.g., back-scattered light, passes through the halfmirror 27, and is introduced to the aforementioned imaging opticalsystem. In this case, depolarization has occurred for the reflectedlight, thereby allowing the reflected light to pass through thereceiving-unit polarizing plate 26, whereby the back-scattered lightreaches the imaging device 24.

The aforementioned scattered or reflected light exhibits phase shift asto the incident light due to birefringence thereof caused by reflectionor scattering in the dermal tissue containing connecting tissue,collagen, and so forth, having properties which cause birefringence ofthe light. Note that the epidermal tissue does not contain theaforementioned materials having properties which cause birefringence ofthe light. With the present embodiment, the system discriminates betweenthe scattered/reflected light from the epidermal tissue and from thedermal tissue (which causes birefringence of the light) by detecting thedifference in the phase of the light therebetween.

Furthermore, an arrangement may be made wherein the system allows onlythe reflected light with a phase shift in a predetermined wavelengthrange due to birefringence in the dermal tissue, to pass through aband-pass filter such as a dichroic filter or the like, and detects onlythe light thus selected, thereby selectively detecting only the tissuewhich causes birefringence of the light, and thereby enabling externalobservation of the dermal tissue in a noninvasive manner.

On the other hand, as an example of measurement of the skin using thepolarizing light, a method is known in the field of the beauty industry,wherein the skin is observed with polarized light using the opticalproperties of a polarizing filter in a range of the visible light. Forexample, a measurement method for evaluating the surface of the skin isknown, wherein the beauty factors such as the glossiness of the skin,the brightness thereof, and so forth, are measured (see JapaneseExamined Patent Application Publication No. 3,194,152, or JapaneseExamined Utility Model Registration Application No. 7-22655).

However, such conventional measurement methods are not configured inorder to observe the tissue beneath the epidermis, such as the dermaltissue or the like, but are configured in order to evaluate the surfaceof the skin using visible light from the perspective of beauty andappearance. That is to say, the disclosed arrangement is nothing but amethod wherein an image of the skin is obtained from scattered lightfrom the skin using visible light while preventing deterioration inimage quality due to the excessive brightness of the reflected lightdirectly reflected from the horny layer of the epidermis or the like,using the well-known nature that depolarization of the light occurs dueto scattering, thereby obtaining a stable image of the skin.

While such conventional methods using visible light have a function ofdetecting the scattered light from the epidermis, use of the visiblelight leads to difficulty in precise detection of the state of thedermal layer due to absorption or interception of the visible light bythe prickle cells or basal cells containing melanin pigment.Furthermore, this leads to difficulty in forming an image by extractinglight wherein birefringence thereof has occurs due to the dermal tissue.No method has yet been proposed whatsoever wherein the structure of thedermal tissue is observed using the fact that the dermal layercontaining the connective tissue, the collagen tissue, and so forth,exhibits great anisotropic optical properties which cause birefringenceof the light as compared with the epidermis, and the fact that theepidermal tissue exhibits high transmissivity of near-infrared light,unlike visible light, i.e., using the scattering properties and thebirefringence properties of the dense connective tissue forming thedermal tissue; this is being newly proposed in the presentspecification.

As described above, the aforementioned detecting device has a functionfor detecting the dermal-layer structure (e.g., the roughnessdistribution pattern) using the scattering properties or thebirefringence properties of the dense connective tissue forming thedermal layer. Note that the detecting device having a configuration asshown in FIG. 2 has the disadvantage of reduction of the SN ratio due toincreased noise due to scattered light from the epidermal layer, andscattered light from the dermal tissue, subcutaneous tissue, and soforth, beneath the surface of the dermal layer which is to be detected.FIG. 3 shows an effective configuration example of the detecting devicefor solving the aforementioned problem, wherein the illumination lightis cast onto the skin with a shallow angle, as well as limiting theaperture of the imaging optical system.

The detecting device shown in FIG. 3 further includes a movingreflecting mirror 28, and has a configuration wherein the illuminationis cast onto the skin in a slant direction from the illumination opticalsystem. Furthermore, the detecting device includes the imaging opticalsystem disposed just above the tissue which is to be measured, therebyenabling direct detection of the back-scattered light and side-scatteredlight without the half mirror 27. Furthermore, the detecting deviceincludes a shield 29 for limiting the aperture, thereby allowing onlythe light returning from the portion just underneath the aperture, toreach the imaging device 24.

With the detecting device having such a configuration, the illuminationlight cast from the illumination optical system passes through thetissue toward the deep-layer structure of the skin (dermal layer) fromthe epidermal layer in a slant direction. In this case, scattering oflight due to an excessively shallow portion, i.e., the epidermal tissue,occurs in the region on the right side shown in the drawing, therebypreventing the scattered light from the excessively shallow portion fromreaching the imaging optical system with the aperture limited by theshield 29. In the same way, scattering of light due to an excessivelydeep portion occurs in the region on the left side shown in the drawing,thereby preventing the scattered light from the excessively deep portionfrom reaching the imaging optical system with the aperture limited bythe shield 29. On the other hand, with the detecting device wherein theangle of the aforementioned moving reflecting mirror 28 is adjusted suchthat the position of the dermal tissue onto which the incident light iscast, is positioned just underneath the aforementioned imaging opticalsystem, only the scattered light from this region (dermal tissue)reaches the imaging optical system.

Next, description will be made regarding a detecting method using thebirefringence of the dermal tissue. First, an arrangement may be madeusing a well-known method for detecting the birefringence, e.g., usingthe optical heterodyne interferometry for converting the phasedifference between the illumination light and the reflected light ortransmitted light into the phase difference in the beat signals, insteadof a method using a band-pass filter as described above.

FIG. 4 is a diagram which shows a mechanism of such an arrangement. Thedetecting device has a configuration wherein the oscillating light iscast to a sample 33 from a light source, e.g., a Stabilized TransverseZeeman Laser (STZL) 31 through a half mirror 32, and the transmittedlight (signal light) passing through a polarizing plate 34 is detectedwith a photo-detector 35. At the same time, a part of the oscillatinglight emitted from the Stabilized Transverse Zeeman Laser 31 isreflected by the half mirror 32, following which the reflected light(reference light) passes through a polarizing plate 36, whereby thereference light is detected with a photo-detector 37. Then, the phasedifference in the light detected by the aforementioned photo-detectors35 and 37 is measured with an electronic phase meter 38.

Here, the linear polarizers (polarizing plates 34 and 36) are used forcausing interference between two light waves. Note that this mechanismenables measurement of the birefringence of the light with precisiondetermined by the electronic phase meter 38. In general, the electronicphase meter 38 exhibits the measurement precision of 0.1 degree (ormore), thereby enabling measurement of the birefringence of the lightwith high precision of approximately 1/4000 of the wavelength of thelight.

Description will be made below regarding a mechanism of the opticalheterodyne interferometry. First, the electric-field component of thereference light Er and the electric-field component of the signal lightEs are represented as follows.

R _(r)=α_(r) cos(2πf _(r) t+φ _(r))   (1)

E _(s)=α_(s) cos(2πf _(s) t+φ _(s))   (2)

Here, a_(r) and a_(s) represent the amplitude of the reference light andthe amplitude of the signal light, respectively. In the same way, f_(r)and f_(s) represent the frequency of the reference light and thefrequency of the signal light, respectively, and φ_(r) and φ_(s)represent the phase of the reference light and the phase of the signallight, respectively.

In general, the light intensity I is represented by the square of theelectric-field component, and accordingly, the light intensity Iobtained by superimposing the two light waves is represented as follows.

$\begin{matrix}\begin{matrix}{I = {\langle{{E_{s} + E_{r}}}^{2}\rangle}} \\{= {\frac{a_{s}^{2} + a_{r}^{2}}{2} + {2a_{s}a_{r}{\cos \left( {{2{{\pi \left( {f_{s} - f_{r}} \right)} \cdot t}} + \left( {\varphi_{s} - \varphi_{r}} \right)} \right)}}}} \\{= {\frac{a_{s}^{2} + a_{r}^{2}}{2} + {2a_{s}a_{r}{\cos \left( {{2\pi \; f_{b}t} + \Delta} \right)}}}}\end{matrix} & (3)\end{matrix}$

Note that in the above expression, the reference symbol “< >” representsthe average over time. On the other hand, f_(b)(=f_(s)−f_(r)) representsthe optical-beat frequency, and the reference character “Δ”(=φ_(s)−φ_(r)) represents the phase difference between two lightcomponents.

The photoelectric current detected with the photo-detector is classifiedinto the DC component represented by the first term and the second termof the Expression (3), and the AC component which changes in the shapeof a sine wave with the frequency fb as represented by the third termthereof. The AC signal will be referred to as “optical-beat signal”.With the optical heterodyne interferometry, the amplitude of theoptical-beat signal (2a_(s)·a_(r)), the frequency (f_(b)), or the phase(Δ), is electrically measured, and the information is obtained basedupon the amplitude (as) of the light signal, the frequency (f_(s)), orthe phase (φ_(s)).

Specifically, with the measurement of the dermal tissue, with therefractive indexes of the skin tissue which causes birefringence of thelight as n_(x) and n_(y), and with the thickness of the tissue which thelight passes through as d, the phase lags φ_(x) and φ_(y) arerepresented by the following Expressions (4) and (5).

$\begin{matrix}{\varphi_{\chi} = \frac{2\pi \; n_{\chi}d}{\lambda}} & (4) \\{\varphi_{y} = \frac{2\pi \; n_{y}d}{\lambda}} & (5)\end{matrix}$

With the present embodiment, the light having two frequency componentsslightly different one from another, such as STZL (Stabilized TransverseZeeman Laser) oscillating light or the like, is cast onto the sample. Inthis case, the light intensity signal I detected by the photo-detectoris represented as follows.

$\begin{matrix}\begin{matrix}{I = {\langle{{E_{x} + E_{y}}}^{2}\rangle}} \\{= {\frac{a_{x}^{2} + a_{y}^{2}}{2} + {2a_{x}a_{y}{\cos \left( {{2{{\pi \left( {f_{x} - f_{y}} \right)} \cdot t}} + \left( {\varphi_{x} - \varphi_{y}} \right)} \right)}}}} \\{= {\frac{a_{x}^{2} + a_{y}^{2}}{2} + {2a_{x}a_{y}{\cos \left( {{2\pi \; f_{b}t} + \Delta} \right)}}}} \\{= {\frac{a_{x}^{2} + a_{y}^{2}}{2} + {2a_{x}a_{y}{\cos \left( {{2\pi \; f_{b}t} + \frac{2{{n\left( {n_{x} - n_{y}} \right)} \cdot d}}{\lambda}} \right)}}}} \\{= {\frac{a_{x}^{2} + a_{y}^{2}}{2} + {2a_{x}a_{y}{\cos \left( {2{\pi \left( {{f_{b}t} + \frac{\delta \; {nd}}{\lambda}} \right)}} \right)}}}}\end{matrix} & (6)\end{matrix}$

Note that reference character “Δ” represents the phase differencebetween the two components of the light, and reference character “δn”represents the difference in the refractive index (=magnitude of thebirefringence). As can be understood from Expression (6), the phasedifference between the two light components is represented by the phasedifference of the beat signals. This enables measurement of themagnitude of the birefringence by measuring the phase of theoptical-beat signals with the electronic phase meter 38 or the like.

Note that with the aforementioned measurement, there is the need todetect the direction of the principal axis beforehand, and to adjust thepolarizing plane of the STZL oscillating light so as to precisely matchthe direction of the principal axis. Accordingly, there is the need tomake measurement wherein the phase difference is detected while rotatingthe polarizing plane of the STZL oscillating light around the opticalaxis, thereby detecting the magnitude of the birefringence as well asthe direction of the principal axis. However, such a measurement methodleads to problems of an extremely complicated configuration of theauthentication device, complicated user operations, and an excessivelylong detecting period of time. Furthermore, in this case, there is theneed to stringently fix the position and the direction of theauthentication device at the time of being fit by the user. Furthermore,the authentication device needs to be closely fit to the body of theuser without looseness so as not to deviate from the fitting positioneven if the user moves.

With the present embodiment, the skin containing a fork structure of thesubcutaneous blood vessel is used as the skin which is to beauthenticated. The direction of the aforementioned principal axis can beeasily obtained using the fork structure. For example, an arrangementmay be made wherein the positional relation between the direction of theprincipal axis and the fork structure is determined and storedbeforehand at the time of user registration, thereby enabling adjustmentof the principal axis at the time of user authentication based upon theposition and the direction of the blood-vessel fork structure in asimple manner.

On the other hand, an arrangement may be made wherein the deep-layerstructure of the skin is detected using interference of the light,thereby solving the aforementioned problems, as well. That is to say,the object of the present invention is not to provide measurement of themagnitude of the birefringence, but it is an object thereof to provide adetecting method for detecting the unique properties of the user bymeasuring the internal structure of the skin through birefringence ofthe light or scattering thereof. With the present arrangement, thesystem causes interference between the incident light and the scatteredlight from the skin without any polarizer, and obtains the change in thefrequency therebetween in the form of beat signals by detecting theinterference of the light, using the fact that upon casting the lightonto the skin, the frequency of the light changes due to back-scatteringof the light or birefringence thereof occurring in the internalstructure of the skin such as the dermal layer or the like.

FIG. 5 shows a configuration example of such a detecting device. Thedetecting device has the same configuration as with the detecting deviceshown in FIG. 2 wherein an illumination optical system formed of anillumination light source 41 and an optical lens 42, and an imagingoptical system formed of an imaging device 43 such as a CCD or the likeand an imaging lens 44, are disposed orthogonal one to another through ahalf mirror 45. Note that with the present arrangement, neither of theillumination optical system and the imaging optical system include apolarizing plate. Instead of the polarizing plates, the presentdetecting device includes a reference mirror 46 for introducing a partof the illumination light cast from the light source 41 of theillumination optical system to the imaging device 43 of the imagingoptical system.

A part of the light emitted from the light source 41 such as a white LEDor the like is cast on the surface of the skin through the half mirror45. Upon casting the aforementioned part of the illumination light ontothe skin, various kinds of scattering of the light and birefringencethereof occur in the internal structure of the skin, and the scatteredlight returns to the half mirror 45. The system causes a beat phenomenon(interference) between the returning light and the light which isreflected from the half mirror 45 onto the reference mirror 46, and isreflected by the reference mirror 46, at the same time of illumination,whereby an interference pattern is formed on the imaging device 43.

Furthermore, an arrangement may be made wherein the aforementioned beatis detected for each region in a detecting range for the skin, therebyobtaining a continuous pattern of the internal structure beneath theepidermis based upon the beat pattern thus obtained. Specificarrangement examples for obtaining the aforementioned continuos patterninclude: an arrangement wherein multiple beat detecting devices arearrayed as shown in FIG. 6; and an arrangement wherein the illuminationunit includes a moving mirror for casting the light onto each region ofthe skin as shown in FIG. 7. The former arrangement has a configurationwherein the multiple beat detecting devices 50 are arrayed in the shapeof a so-called “array”, each of which comprise the illumination opticalsystem formed of the aforementioned illumination light source 41 and theoptical lens 42, and the imaging optical system formed of the imagingdevice 43 such as a CCD or the like and the optical lens 44, disposedorthogonal one to another through the half mirror 45, thereby obtaininga continuos pattern of the internal structure beneath the epidermisbased upon the signals detected with each beat detecting device 50.

On the other hand, with the latter arrangement, illumination of thelight and detection of the returning light with each beat detectingdevice 50, are performed using the aforementioned moving mirror 51. Thelatter arrangement has a configuration wherein a mirror control unit 52controls the angle of the moving mirror 51 according to controlinformation from an angle/interference-pattern adjusting unit 53. Theaforementioned angle/interference-pattern adjusting unit 53 receivesinterference-pattern information from the aforementioned beat detectingdevice 50. Then, the received interference pattern is compared to aninterference pattern which has been stored and registered beforehand ina skin-interference pattern storage unit 54, in a skin-interferencepattern storage/comparison unit 55, thereby enabling biometricauthentication.

The aforementioned methods do not require a polarizer which isindispensable for detection of the phase difference or the like, therebyhaving the advantage of enabling authentication without preciseadjustment of the optical axis. This allows stable authentication evenif the direction of a wristwatch-type authentication device or the like,fit by the user, changes due to failure in being fit by the user,looseness at the time of being fit by the user, or the like, forexample.

In practical situations, there is the need to adjust the authenticationdevice so as to face the tissue which is to be authenticated in a casewherein the authentication device is fit by the user with somelooseness, or the like. On the other hand, an arrangement may be madewherein the interference pattern is registered for a wide skin regionincluding the target region. However, such an arrangement requirespattern matching processing for searching the aforementioned wide regionfor a matched pattern, leading to a great processing load. Such a greatload is undesirable for a mobile authentication device from theperspective of power consumption and so forth.

For example, let us consider a special case of the biometricauthentication using the skin pattern, such as fingerprints or the like.In this case, the center of a whirl-shaped pattern, a horseshoe-shapedpattern, or the like, can be easily detected, and furthermore, the areaof the surface of the finger having such a structure is narrow, therebyfacilitating search for the position which is to be authenticated.However, other ordinary portions have relatively large area as comparedwith the fingertip, and have fine skin pattern having no geometricstructure which facilitates search for the position which is to beauthenticated, unlike the whirl-shaped pattern of the fingerprints,except for limited special portions, leading to extreme difficulty insearch for the region which is to be authenticated.

In order to solve the aforementioned problem, an arrangement may be madewherein the skin pattern is registered for a wide region beforehand asdescribed above, and the system determines whether or not the patterndetected at the time of authentication is included in the aforementionedregistered pattern. However, such an arrangement leads to registrationfor an excessively large area, which is troublesome, and leads to aproblem of excessive processing load and excessive processing period oftime of the authentication device at the time of authentication. With anideal arrangement, the skin pattern is preferably registered for thewhole body. However, such an arrangement is not undesirable from thepractical perspective as described above. Furthermore, in this case, itis difficult to determine the “wide region”. In practical situations,the authentication device may deviate from the region at the time ofauthentication due to flexibility of the human body, or difference inthe position to which the authentication device is fit for eachauthentication.

Description will be made below regarding an effective method forsearching for the target region of the skin which is to beauthenticated. With the present method, the near-infrared light isemployed as the incident light instead of white light, which has awavelength range which allows the light to pass through the tissue withhigh transmissivity, and causes exceptional absorption of the light byreduced hemoglobin contained in venous blood or the like. Theauthentication device detects a vein pattern using the detectedback-scattered light from the subcutaneous tissue, and searches for thetarget region which is to be authenticated based upon the vein patternthus obtained. With the present arrangement, the target region which isto be authenticated is a region containing a distinctive pattern or avein fork structure. This allows stable search for the same skin regionwhich is to be authentication in a sure manner, even if awristwatch-type person authentication device is fit by the user withsome displacement or looseness on a contact face between theauthentication device and the skin of the user.

FIG. 8 shows an example of a detecting device having a function forsearching for the target region which is to be authenticated based uponthe vein pattern. The detecting device shown in FIG. 8 has the sameconfiguration as in FIG. 7, except for a configuration wherein anear-infrared light source is employed as the light source 41 for thebeat detecting device 50, and a subcutaneous vein position detectingunit 61, a subcutaneous vein position comparison unit 62, and a veindata storage unit 63 for storing vein data, are further included. Such aconfiguration allows acquisition of an image of blood capillaries of asubcutaneous vein 60 extending along the dermal layer, which is a veinpositioned at the shallowest portion of the skin.

The tissue exhibits marked low absorbance for the infrared light in awavelength range of 700 to 1200 nm, i.e., the tissue has propertieswhich allow the light to readily pass therethrough, and accordingly, thewavelength range is referred to as “the window of spectroscopicanalysis”. Note that while the epidermal tissue has the properties whichcause reflection and scattering of visible light and ultraviolet light,nearly approximately 80% of the light in the aforementioned wavelengthrange passes through the tissue. On the other hand, of the near-infraredlight in such a wavelength range having such properties, thenear-infrared light at a particular wavelength is selectively absorbedby hemoglobin contained in blood. Specifically, as shown in FIG. 9, theoxidized hemoglobin (HbO₂) exhibits the same absorbance as with thereduced hemoglobin (Hb) at a wavelength of 805 nm. On the other hand,the reduced hemoglobin (Hb) exhibits higher absorbance than with theoxidized hemoglobin (HbO₂) at a wavelength of 660 nm, and the oxidizedhemoglobin (HbO₂) exhibits higher absorbance than with the reducedhemoglobin (Hb) at a wavelength of 940 nm. Furthermore, the hemoglobinhas different spectroscopic properties from those of water in thetissue, as shown in FIG. 10.

Accordingly, a blood-vessel image can be obtained by detectingdifference between hemoglobin and water within the tissue using theaforementioned properties. Furthermore, difference between an artery anda vein can be detected using difference in absorbance therebetween at asuitably-selected wavelength. In order to detect a vein pattern, anarrangement may be made wherein the light source includes illuminationmeans for illuminating near-infrared light with a wavelength of 805 nm,and the near-infrared light is cast onto the tissue through a polarizingplate, for example. The incident light causes three kinds of phenomenaof reflection of the light, scattering thereof, and birefringencethereof, and the returning light due to the aforementioned kinds ofphenomena is detected. In this case, the reflected light from thesurface of the skin deteriorates the quality of the image of theinternal structure beneath the skin surface. Accordingly, with thepresent arrangement, an image of the internal structure is taken with aCCD camera or the like through the polarizing plate 26 disposed with thepolarizing plane orthogonal to that of the polarizing plate 23. Thisallows image taking using only depolarized light such as scattered lightand light split due to birefringence while filtering the reflected lightwith the same polarizing plane as with the incident light, which hasbeen reflected by the horny layer, the lucid layer, the granular layer,and so forth, forming the epidermal tissue.

While description has been made regarding the detecting devices shown inFIG. 2 and FIG. 3, wherein the dermal layer is detected by eliminatingthe returning light other than the scattered light from the tissue whichis to be detected, with the present arrangement, the incident light witha suitably-selected wavelength is selectively absorbed in bloodcapillaries within the dermal layer since the materials in blood vesselswithin skin tissue other than hemoglobin exhibit low absorbance, i.e.,have high transmissivity at the wavelength, unlike a case of using thewhite light source, thereby obtaining a clear image of a blood-capillarypattern within the dermal layer with back-scattering of the light at adeeper portion as a background.

The pattern formed of blood flow in the blood capillaries is unique toindividual tissue. Furthermore, in the event that the tissue is cut offfrom the body of the user, the aforementioned pattern is immediatelylost due to contraction of blood vessels, retention of blood, lost ofblood, and so forth. Furthermore, an arrangement may be made wherein thesystem detects change in absorbance corresponding to the heart beatusing the absorbance of oxidized hemoglobin at a wavelength of 940 nm,thereby enabling living-tissue discrimination, as well as acquisition ofan image of the pattern of the subcutaneous blood capillaries.Furthermore, the present arrangement may include an additional methodwherein determination is made whether the tissue belongs to normal livetissue or dead tissue cut off from the user by detecting reduction orloss of the absorbance of oxidized hemoglobin at a wavelength of 940 nmdue to extreme reduction of oxygen concentration within the tissue dueto failure in pulmonary circulation, using the fact that different typesof hemoglobin exhibit different absorbance, e.g., the fact that thedeoxidized hemoglobin exhibits higher absorbance than with the oxidizedhemoglobin at a wavelength of 660 nm, the fact that the oxidizedhemoglobin exhibits higher absorbance than with the deoxidizedhemoglobin at a wavelength of 940 nm, and so forth.

The aforementioned methods integrate the biometric authentication andthe living-tissue discrimination. That is to say, the system candiscriminate and reject the tissue cut off from the body of the user bydetecting absence of blood flow even if the tissue is alive by soakingin a physiological salt solution. In this case, the tissue which is tobe authenticated needs to exhibit normal pulmonary circulation, normalheart beat, normal blood flow, and normal hemoglobin ratio in blood.Accordingly, if other persons cut off the arm of the user with asurgical method for “spoofing”, there is the need to connect the bloodvessels of the arm to a heart-lung machine, and to precisely reproducethe heat-beat wave. Accordingly, it would be difficult to make“spoofing” in the present situation wherein mobile heart-lung machinesare unavailable. Even if mobile heart-lung machines become available inthe future, such “spoofing” would require advanced surgical techniquesand surgical equipment for performing: cutting off of the arm from thebody; connection of the blood vessels of the arm to a heart-lungmachine; treatment for fine blood vessels and nerves; prevention ofchange in the tissue due to vital reaction caused due to cutting off ofthe arm; stabilization of the tissue after resumption of blood flow; andso forth, which is far from being realistic. On the other hand, it iseven more difficult to create a forgery of the tissue having preciselythe same three-dimensional structure of fine blood capillaries whichcauses the same scattering of the light, instead of the tissue cut offrom the body of the user.

Next, description will be made regarding a detecting method fordetecting a pattern beneath the epidermis using the differentialinterference method. The differential interference method is one ofobservation methods using a microscope, wherein the phase differencebetween the illumination light and the returning light, which isdependent upon the thickness of the sample and the difference in therefractive indexes, is converted into contrast or contrast in color,thereby enabling observation which provides impression of solidity. Ingeneral, it is difficult to detect the dermal layer through a brightfield optical system or visual observation. The present arrangement hasbeen made using the fact that a differential interference optical systemallows the user to observe even cell nuclei wherein observation isdifficult using an ordinary microscope without staining. Note that whilethe aforementioned differential interference optical system allowsdetection of the dermal layer in a case wherein the dermal layer appearsas a top layer, it is difficult to detect the dermal layer in normalsituations. That is to say, in normal situation wherein the dermal layeris covered with the epidermal layer, while the surface of the epidermallayer can be observed with such a method, detection of the epidermallayer is difficult due to reflection of light, scattering thereof, andshielding thereof, without some particular method.

While a white light source is employed for an ordinary differentialinterference optical system, with the present invention, a near-infraredlight source and a near-infrared CCD are employed as well as adifferential interference optical system, using the fact that theepidermal layer exhibits high transmissivity in a wavelength length ofred light to near-infrared light. This enables detection of theroughness pattern of the dermal layer beneath the epidermis in anoninvasive manner.

FIG. 11 shows a specific arrangement example. A detecting devicecomprises an illumination optical system including a near-infrared lightsource 71, a polarizing prism 72, and an imaging optical systemincluding an imaging device 73 such as a CCD or the like, and apolarizing prism 74. The illumination optical system and the imagingoptical system are disposed with the optical paths orthogonal one toanother through a half mirror 75. The illumination light is cast ontothe skin from the illumination optical system through reflection by thehalf mirror 75, and the returning light (reflected light) passes throughthe half mirror 75, whereby the light reaches the imaging opticalsystem. Note that a Wollaston prism 76 and an objective lens 77 aredisposed on the optical path between the aforementioned half mirror 75and the skin.

The illumination light cast from the near-infrared light source 71 isconverted into light with the same polarizing plane by the polarizingprism 72, and is reflected by the half mirror 75 toward the Wollastonprism 76. The illumination light cast onto the Wollaston prism 76 issplit into two beams (beam A and beam B) with the polarizing planesorthogonal one to another, following which the two beams are cast ontothe object (tissue). Note that the distance between the beam A and thebeam B is equal to or less than the resolution of the objective lens.Subsequently, the two beams reflected by the object are recombined intoa single beam by the Wollaston prism 76. The single beam thus recombinedpasses through the half mirror 75, and is converted into the light withthe same polarizing plane by the polarizing prism 74. With such aconfiguration, reflection of the two beams A and B at a stepped portionleads to optical-path difference therebetween, leading to interferencethereof at the time of the beam passing through the polarizing prism 74.Note that in a case wherein the optical-path difference matches half thewavelength of the beams A and B, the light appears brightest due tointerference. The interference pattern can be observed with an ordinarydifferential interference optical system employing a white light source,thereby enabling the user to make visual observation of a transparentobject with impression of solidity. However, with the presentarrangement using near-infrared light, visual observation is difficult.Accordingly, the present arrangement includes the imaging device 73 suchas a CCD for taking a near-infrared image.

[Method Using the Electric Properties]

Next, description will be made regarding another method according to thepresent invention, wherein the roughness pattern or the like of thedeep-layer structure (e.g., the dermal tissue) beneath the epidermisusing the difference in the electric properties, whereby biometricauthentication is performed.

FIG. 12 shows an arrangement example of a detecting device wherein theelectric potential of the skin is detected using electrostaticinduction, and the depth at which the dermal tissue is positioned isdetected based upon the detected electric potential, whereby theinternal pattern beneath the epidermis is obtained. With the presentdetecting device, the electrostatic capacitance between the detectingelectrode and the dermal layer is detected using the fact that theepidermal layer relatively exhibits a nature near being dielectric whilethe dermal layer exhibits high electric conductivity.

In order to detect the electrostatic capacitance, the detecting deviceshown in FIG. 12 includes multiple fine electrodes 121 two-dimensionallyarrayed with micromachining technology so as to form a detectingelectrode plane for being in contact with the surface of the skin. Atthe time of measurement, electrostatic capacitance is formed betweeneach fine electrode 121 on the detecting electrode plane and the dermallayer. Then, the distance distribution regarding the subcutaneouselectric-conductive layer underneath each fine electrode 121 iscalculated based upon the electrostatic capacitance which is dependentupon the distance between the electrode and the electric-conductivelayer, thereby obtaining the subcutaneous tissue structure. That is tosay, with the present detecting device, electrostatic capacitance isformed between: each of the fine electrodes 121 forming the detectingelectrode plane positioned parallel to the skin; and the skin, and theterminal voltage of each electric capacitance is measured, whereby thedermal-layer structure is obtained.

A cylindrical metal casing 22 stores the aforementioned fine electrode121 held by an insulating support member 123. The fine electrode 121 iselectrically connected to the casing 22 through a resistor 24 havinghigh electrical resistance. There is a gap between the fine electrode121 and the casing 122. At the time of the casing 122 being in contactwith the skin, the aforementioned fine electrode 121 faces the skin witha predetermined gap therebetween at an opening 122 a of the casing 122.

Note that the present detecting device has a problem of extremelyunstable output signals since the surface of the skin having the naturenear a dielectric is readily affected by electrostatic induction due tonoise or the like from an external AC power supply or a fluorescentlamp, and the surface structure of the skin readily exhibits variousconditions due to separation of the horny layer, or the like. In orderto solve the aforementioned problem, a method is known for detectingfingerprints or the like, wherein output signals are detected whileapplying high-frequency electric signals to the human body. Such amethod may be applied to detection of the tissue structure wherein theepidermal pattern corresponds to the dermal pattern, such as thefingerprints or the like. However, the aforementioned method cannot beapplied to detection of the dermal pattern of other skin tissue whereinthe epidermal pattern does not correspond to the dermal pattern. Thereason is that in this case, the detecting device detects the epidermalpattern. The epidermal pattern which does not correspond to the dermalpattern does not exhibit sufficient stability, unlike the fingerprints,and accordingly, the aforementioned method cannot be employed for thebiometric authentication using detection of such tissue.

Accordingly, in order to solve the aforementioned problems, thedetecting device according to the present arrangement includes adielectric thin film 125 disposed at the opening of the metal casing 122as shown in FIG. 13, for example. At the time of measurement, thedielectric thin film 125 is positioned between the metal casing 122 andthe skin with which the detecting device is pressed into contact. At thesame time, the dielectric thin film 125 is in contact with the metalcasing 122 which stores the fine electrode 121 and is connected to theground, whereby electrostatic capacitance is formed between casing 122and the skin, as well. Furthermore, such a configuration has theadvantage of suppressing adverse effects due to unstable conditions ofthe surface structure of the horny tissue of the skin.

Furthermore, the detecting device includes an electret film 126 on thesurface of each fine electrode 121 forming the detecting electrodeplane. The electret film 126 is formed of a tetrafluoroethylene film orthe like and semi-permanently holds electric charges. With the presentarrangement, the electrostatic capacitance is formed between the fineelectrode 121 and the dermal tissue (electrically conductive tissue)with a bias voltage due to the permanent polarization of the electretfilm 126 without externally applying high frequency bias voltage,thereby enabling detection of the distribution of difference in theelectrostatic capacitance between the fine electrodes 121, and therebyenabling detection of the deep-layer structure of the skin such as thedermal layer or the like covered with the epidermal tissue of the skinin a noninvasive manner.

With the detecting device having a configuration shown in FIG. 13, thefine electrode 121 having the electret film 126 is disposed at theopening 122 a of the aforementioned casing 122. At the time ofmeasurement, the detecting device is positioned such that the opening122 a faces the tissue, whereby electrostatic capacitance is formedbetween the fine electrode 121 and the skin through the dielectric thinfilm 125. On the other hand, the casing 122 serves as a counterelectrode as to the skin, and is grounded. On the other hand, theelectrode within the opening 122 a serves as a detection electrode.Accordingly, change in the electric potential due to the epidermaltissue is common to both the electrodes, and accordingly, the componentsthereof exhibit reverse polarity between both the electrodes, leading tocanceling out one another.

On the other hand, change in the electric potential at a deep portion ofthe skin causes electrostatic capacitance between the dermal layerhaving electric conductivity and the fine electrode 121 serving as adetection electrode, thereby enabling detection of change in theelectric potential at the deep portion of the skin. On the other hand,no bias voltage due to an electret film or the like is applied to thecapacitance formed by the casing 122, and accordingly, change in theelectric potential of the deep layer of the skin is not detected bymeasuring the capacitance formed by the casing 122 due to charges on thesurface of the skin. Thus, the present arrangement allows the detectingdevice to precisely detect changes in the electric potential of the deeplayer of the skin alone, while canceling out adverse effects due toelectrostatic induction of the skin surface, charges thereon, or thelike.

With an arrangement wherein the change in the electric potential ismeasured by extracting from change in the electrostatic capacitance ateach point on the tissue, different amplitude is detected for each pointdue to variation in the electrostatic capacitance dependent upon thethickness of the epidermis. FIG. 14 shows an arrangement having aconfiguration wherein the aforementioned detection electrodes (fineelectrodes 121) are two-dimensionally arrayed in the form of a matrix,and having a function wherein the conductive-layer structure beneath theepidermis is obtained using the amplitude of the electric potentialwhich is changed synchronously with the entire human body due to walkingor the like.

As shown in FIG. 15, at the time of walking, change in the electriccharge occurs with a single phase, synchronously with the entire humanbody due to grounding and electrical floating between the foot and thefloor. Description will be made below regarding change in charge on thehuman body due to walking. That is to say, the waveform which is formedon the skin due to walking and is detected by anelectrostatic-capacitance sensor, is formed according to two mechanismsas follows.

The first mechanism is essentially the same as with a capacitormicrophone. The capacitor microphone has a mechanism wherein the gapbetween a diaphragm and an electret electrode changes due to vibrationof the diaphragm, the electrostatic capacitance (C) of the gap changesdue to the vibration, and the signals due to change in the electrostaticcapacitance are subjected to impedance conversion through the gate of anFET, whereby the vibration of the diaphragm is detected. The detectingdevice according to the present invention has the same configuration aswith the capacitance microphone, except for the configuration wherein adielectric film is included instead of the diaphragm, which is pressedinto contact with the tissue of the human body at the time ofmeasurement, whereby charge coupling occurs between the detecting deviceand the tissue of the human body through the dielectric film. At thesame time, capacitance (electrostatic capacitance) is formed by the gapbetween the electret electrode and the dielectric film, and furthermore,the electrostatic capacitance of the human body and the electrostaticcapacitance of the gap are combined due to charge coupling. In thisstate, change in the electrostatic capacitance due to interactionbetween the human body and the external environment (e.g., groundedobject), e.g., walking or the like, is directly detected by thedetecting device in the form of waveform signals, like the capacitancemicrophone.

Here, the electrostatic capacitance (C) of the human body changescorresponding to the distance between the ground and the position of thefoot in the space. That is to say, in a case wherein the foot is incontact with the ground, the capacitance of the human body is great. Onthe other hand, in a case wherein the foot is positioned away from theground, the electrostatic capacitance of the human body is extremelysmall due to an air layer having a low dielectric constant between thesole (of a shoe) and the ground. On the other hand, the greater thecontact area between the foot and the ground, the grater theelectrostatic capacitance is. Note that the electrostatic capacitance Cis represented by the following Expression.

C=ε·S/d [F] (ε represents dielectric constant of a medium with which thegap between the electrodes is filled, S represents the area of theelectrode, and d represents the distance between the electrodes)

As can be understood from the above Expression, the greater the contactarea between the foot and the ground is, i.e., the greater the area ofthe electrode (S) is, the greater the electrostatic capacitance is.

The second mechanism is that the electrode itself makes an actionserving as a charge sensor. That is to say, the electrode stored in themetal casing of the detecting device, which faces the tissue through thedielectric film, detects change in the electric potential induced on thedielectric film due to charge of the human body in the form of awaveform.

It is assumed that the waveform detected on the human body is formedaccording to the two mechanisms as described above, i.e., it is assumedthat the waveform is essentially formed not due to the electricpotential, but due to charge. That is to say, it is assumed that thephenomenon represented by the following Expression occurs. Note that theassumption has been confirmed by reproducing the observed waveform bysimulation using the equivalent circuit method.

Q (charge)=C (electrostatic capacitance)·V (voltage of the electrode)

While change in the aforementioned charge exhibits generally the samewaveform over the entire human body, the waveform exhibits differentamplitude corresponding to the fine structure of the skin tissue, inparticular, corresponding to the relation between the epidermis and thedermal layer. The waveform due to change in charge changes synchronouslyover the entire human body. Accordingly, with the present arrangement,comparison is made for the amplitude of the waveform detected by each ofthe fine detecting electrodes arrayed in the form of a two-dimensionalmatrix, thereby measuring the distance between the electrode and thedermal layer for each electrode, and thereby obtaining the structurebeneath the epidermis.

As described above, with the present arrangement, change in chargeoccurring due to walking or other motions is detected with each fineelectrode 121 without active charge generating means such as anelectrode for applying charges or the like, using the fact that chargechanges on the human body due to interaction between the foot and theground by motions wherein the foot is off the ground and touches theground at the time of walking or the like. Then, the difference in theamplitude between the waveforms occurring due to change in chargesynchronously over the entire human body due to motions of the user isconverted into the distance between the surface of the skin and thetissue beneath the epidermis, thereby detecting the deep-layer structurebeneath the epidermis such as the dermal layer or the like underneaththe detecting electrode.

In general, it is assumed that conventional electrostatic-capacitancemethods have been applied to a stationary authentication device which isgrounded. Accordingly, at the time of a wearable authentication deviceemploying such a conventional method being fit by the user forperforming authentication of the user, in a case wherein the user walkson a carpet in a low humidity environment in winter, both the detectingelectrode and the grounded portion may be greatly charged, leading todifficulty in precise detection. The reason is that with the wearableauthentication device, the grounded portion is positioned on the humanbody.

In order to solve the aforementioned problems, a method or the like hasbeen proposed, wherein additional transmission means such as anelectrode, a transducer, or the like, is provided for being in contactwith the human body in addition to the detecting electrodes, apredetermined ultrasonic waves or high-frequency signals are activelyapplied with the transmission means so as to propagate on the humanbody, the signals thus propagating on the human body are detected withfine electrodes on the skin, and determination is made whether or notthe face of each fine electrode is in contact with the skin, therebyobtaining the fingerprint pattern of the user. However, such a methodleads to a complicated configuration, as well as leading to a problemthat the tissue which is to be authenticated is restricted to a specialportion such as fingerprints, a part of the skin of the palm, and soforth. For example, let us consider an authentication method wherein theauthentication is performed using the skin underneath a ring including abuilt-in authentication device. In this case, the pattern of theepidermal layer at such a portion, such as wrinkles or the like, tendsto be formed different from the pattern of the dermal layer, in somecases, orthogonal thereto. That is to say, with such a method, theepidermal pattern having poor stability is detected, leading to problemof poor precision of authentication.

On the other hand, with an arrangement according to the presentinvention, the epidermal pattern is not detected, but the structure ofthe tissue beneath the epidermis (e.g., the roughness pattern of thedermal layer) is detected by measuring electrostatic capacitance asdescribed above, thereby solving all the aforementioned problems.

That is to say, with the present invention, biometric authentication isperformed by detecting the structure of the tissue beneath theepidermis, and accordingly, the “biometric authentication” and the“living-tissue discrimination” are integrated. Accordingly, the systemcan discriminate and reject the tissue cut off from the body of the userby detecting absence of blood flow even if the tissue is alive bysoaking in a physiological salt solution. Furthermore, the tissue whichis to be authenticated needs to exhibit normal pulmonary circulation,normal heart beat, normal blood flow, and normal hemoglobin ratio inblood. Accordingly, if other persons cut off the arm of the user with asurgical method for “spoofing”, there is the need to connect the bloodvessels of the arm to a heart-lung machine, and to precisely reproducethe heat-beat wave. Accordingly, it is difficult to make “spoofing” inthe current situation wherein mobile heart-lung machines areunavailable. If the mobile heart-lung machine becomes available in thefuture, such “spoofing” would require advanced surgical techniques andsurgical equipment for performing: cutting off of the arm from the body;connection of the blood vessels of the arm to a heart-lung machine;treatment for fine blood vessels and nerves; prevention of change in thetissue due to vital reaction caused due to cutting off of the arm;stabilization of the tissue after resumption of blood flow; and soforth, which is far from practical. On the other hand, it is moredifficult to create a forgery of the tissue having precisely the samethree-dimensional structure of fine blood capillaries which causes thesame scattering of the light, instead of the tissue cut of from the bodyof the user.

Furthermore, the present invention may be applied to a wearablearrangement. For example, an arrangement may be made wherein a wearableinformation device or a mobile information device includes detectingmeans for detecting the pattern of tissue, blood vessels, or the like,beneath the epidermis wherein visual observation is difficult undernatural light, on the face thereof for being in contact with the skin ofthe user at the time of the user holding or wearing the informationdevice, the skin-tissue pattern beneath the epidermis on the contactface between the body of the user and the information device is detectedat the time of the user holding or wearing the information device, thedetected pattern is compared to the patterns which have been registeredin the information device or a server computer connected to theinformation device via network, thereby enabling the system to permit orrestrict at least a part of the service provided from the informationdevice or the network system based upon the detection results, i.e.,thereby enabling so-called “access control”.

Let us consider that the present invention is applied to a wearableauthentication device such as wristwatch-type authentication device, orthe like, for example. In this case, there is the need to strictly fixthe position and the direction of the authentication device at the timeof being fit by the user. Furthermore, the authentication device needsto be closely fit to the body of the user without looseness so as not tobe deviated from the fitting position even if the user moves.Specifically, the system needs to determine the portion of the skinwhich is to be authenticated. On the other hand, an arrangement may bemade wherein the interference pattern is registered for a wide skinregion including the target region. However, such an arrangementrequires pattern matching processing for searching the aforementionedwide region for a matched pattern, leading to a great processing load.Such a great load is undesirable for a mobile authentication device fromthe perspective of power consumption and so forth.

For example, let us consider a special case of the biometricauthentication using the skin pattern, such as fingerprints or the like.In this case, the center of a whirl-shaped pattern, a horseshoe-shapedpattern, or the like, can be easily detected, and furthermore, the areaof the surface of the finger having such a structure is narrow, therebyfacilitating search for the position which is to be authenticated.However, other ordinary portions have relatively large area as comparedwith the fingertip, and have fine skin pattern having no geometricstructure which facilitates search for the position which is to beauthenticated, unlike the whirl-shaped pattern of the fingerprints,except for limited special portions, leading to extreme difficulty insearch for the region which is to be authenticated.

In order to solve the aforementioned problem, an arrangement may be madewherein the skin pattern is registered for a wide region beforehand asdescribed above, and the system determines whether or not the patterndetected at the time of authentication is included in the aforementionedregistered pattern. However, such an arrangement leads to registrationfor an excessively large area, which is troublesome, and leads to aproblem of excessive processing load and excessive processing period oftime of the authentication device at the time of authentication. With anideal arrangement, the skin pattern is preferably registered for thewhole body. However, such an arrangement is not undesirable from thepractical perspective as described above. Furthermore, in this case, itis difficult to determine the “wide region”. In practical situations,the authentication device may deviate from the region at the time ofauthentication due to flexibility of the human body, or difference inthe position to which the authentication device is fit for eachauthentication.

In order to solve the aforementioned problems, the skin containing afork structure of the subcutaneous blood vessel is preferably used asthe skin which is to be authenticated. The direction of theaforementioned principal axis can be easily obtained using the forkstructure. For example, an arrangement may be made wherein thepositional relation regarding the fork structure is determined andstored beforehand at the time of user registration, thereby enablingadjustment of the portion of the skin which is to be authenticated atthe time of user authentication based upon the position of theblood-vessel fork structure in a simple manner.

[Method Using Temperature Difference]

Next, description will be made regarding detection of the tissue patternand authentication using temperature difference. The skin structurecomprises the epidermal tissue which has no blood vessels and is passiveto the body temperature, and the dermal tissue which has blood vesselsand actively affects the temperature through blood flow. This causes arelatively high temperature in the dermal tissue as compared with theepidermal tissue, except for special situations wherein heat isexternally applied, such as exposure of direct sunlight to the bodysurface. A detecting device according to the present embodiment detectsthe structure of tissue beneath the epidermis using the aforementionedmechanism.

For example, the detecting device according to the present embodimenthas a configuration wherein fine devices for detecting temperature suchas thermistor bolometers, thermopiles, or the like, aretwo-dimensionally arrayed instead of the fine electrodes describedabove, and temperature is measured at each point. In this case,difference in temperature is detected between the fine devicescorresponding to the thickness of the epidermal layer or the likeunderneath each fine device. The detecting device according to thepresent embodiment detects the roughness structure of the dermal layerbeneath the epidermis using the aforementioned mechanism. In particular,thermopiles having a sensitive range corresponding to infrared lightemitted from the human body are preferably employed as the fine devicesfor detecting temperature, thereby enabling detection while preventingadverse effects due to an external heat source such as sunlight or thelike.

Furthermore, an arrangement may be made wherein infrared-light detectingmeans, which is a temperature detecting means, are disposed in the formof a matrix, and the detecting face thus formed is positioned close tothe surface of the skin, thereby detecting the dermal layer patternbeneath the epidermal tissue, using the fact that the living tissueemits infrared light with a unique wavelength (e.g., wavelength ofaround 10 μm) due to the body temperature. With the present arrangement,a difference in the infrared magnitude is detected between the infrareddetecting sensor units forming the matrix-shaped infrared detectingmeans, corresponding to the thickness of the epidermis or the distancebetween the sensor unit and the dermis serving as an infrared source.The detecting device according to the present arrangement detects thestructure of the subcutaneous tissue, e.g., the roughness pattern of thedermal layer, based upon the infrared magnitude distribution.

Furthermore, an arrangement may be made wherein the positions of theblood vessels are detected using the fact that a portion containing thesubcutaneous blood vessels exhibits a relatively high temperature ascompared with the other portions, thereby enabling biometricauthentication. Furthermore, an arrangement may be made wherein theposition or the direction of the portion which is to be authenticated isdetermined based upon a detected image of blood capillaries.Furthermore, living-tissue discrimination may be performed based upon adetected image of blood capillaries, as well.

INDUSTRIAL APPLICABILITY

As can be clearly understood from the above description, the presentinvention enables ubiquitous biometric authentication using not only aspecial portion such as the fingertip or the like, but also any desiredportion of the skin of the user. Furthermore, such a portion which is tobe authenticated cannot be observed from the outside, unlike thefingerprints, and accordingly, it is difficult for other persons toidentify the portion of the user body which is used for authentication.Thus, the present invention has the advantage of high security ofprivacy, as well as the advantage of high security against forgery.

Furthermore, the present invention provides an authentication methodusing the portion having active blood flow or active circulation of bodyfluid, such as the dermal tissue. The properties of such a portionexhibits high sensitivity to change in the blood flow or circulation ofbody fluid, thereby providing essential and complete integration ofbiometric authentication means and living-tissue discrimination. Thus,the present invention provides biometric authentication whilesuppressing the risk of surgical hazard, i.e., improving safety of theuser.

Furthermore, the present invention may be applied to a wearabledetecting device and a wearable authentication device having a detectingportion for being in contact with the skin of the human body, therebyenabling biometric authentication using daily actions of the userwithout any special user operations. Furthermore, even in the event thatdetection error or authentication error occurs, retry processing isperformed without any particular user operations, and is nottroublesome.

1. A blood vessel authentication apparatus, comprising: a light emittingsection configured to emit near-infrared source light in a predetermineddirection toward a part of a person, said part having an epidermal layerand a deep layer beneath said epidermal layer, said deep layer havingblood vessels that carry blood, said predetermined direction beingslanted relative to a normal direction of a target portion of said part;an imaging section configured to detect scattered light which is aportion of said source light that has penetrated the epidermal layer andis scattered by tissue in said deep layer, said tissue in said deeplayer scattering light such that less light is detected in regionscorresponding to the blood vessels than other regions without the bloodvessels; an authentication section configured to authenticate anidentity of a person associated with the part based on a comparison ofthe scattered light detected by said imaging section and blood vesselinformation previously stored; and a shield for limiting an aperture ofthe imaging section, wherein the shield is adapted to shield the imagingsection from light scattered in a layer of said part other than saiddeep layer.
 2. The apparatus according to claim 1, wherein the part ofthe person is a finger.
 3. The apparatus according to claim 1, whereinthe imaging section detects the scattered light arriving from adifferent direction than said predetermined direction.
 4. The apparatusaccording to claim 1, wherein the blood vessel information comprisesblood vessel position information.
 5. The apparatus according to claim1, wherein the blood vessel information comprises blood vessel patterninformation.
 6. The apparatus according to claim 1, further comprising astorage device configured to store said blood vessel information.
 7. Theapparatus according to claim 1, further comprising an interface forconnecting via a network to a storage device that holds said bloodvessel information.
 8. The apparatus according to claim 1, wherein thelight emitting section emits near-infrared source light at a wavelength,at which the absorbance of oxidized hemoglobin and reduced hemoglobin isthe same.
 9. The apparatus according to claim 1, wherein the lightemitting section emits near infrared source light at a wavelength, atwhich the absorbance of oxidized hemoglobin and reduced hemoglobin isdifferent.
 10. The apparatus according to claim 1, further comprising areference mirror, onto which the light emitting section emitsnear-infrared source light, wherein the apparatus detects a beatphenomenon between light, which is reflected from the reference mirror,and the detected scattered light, which is a portion of said sourcelight that has penetrated the epidermal layer and is scattered by tissuein said deep layer.
 11. The apparatus according to claim 10, furthercomprising: a moving mirror; and a mirror control that controls an angleof the moving mirror, such that near-infrared source light emitted bythe light emitting section is cast in multiple directions towardsmultiple regions of said part of a person, and wherein the beatphenomenon is detected for each region.
 12. The apparatus according toclaim 10, wherein the authentication section comprises anangle/interference-pattern adjusting unit, which is adapted to receiveinformation on the detected beat phenomenon and to compare the beatphenomenon of one or more regions to beat phenomena that are stored inthe pattern storage device, in order to enable biometric authentication.13. A blood vessel authentication method, comprising steps of: storingblood vessel information; emitting near-infrared source light in apredetermined direction toward a part of a person, said part having anepidermal layer and a deep layer beneath said epidermal layer, said deeplayer having blood vessels that carry blood, and said predetermineddirection being slanted relative to a normal direction of a targetportion of said part; detecting scattered light which is a portion ofsaid source light that has penetrated the epidermal layer and isscattered by tissue in said deep layer, said tissue in said deep layerscattering light such that less light is detected in regionscorresponding to the blood vessels than other regions without the bloodvessels; authenticating an identity of the person associated with thepart, said authenticating including comparing a detection result of saiddetecting step with said blood vessel information; and shielding anaperture of the imaging section from light scattered in a layer of saidpart other than said deep layer.
 14. The method according to claim 13,wherein said storing step includes storing said blood vessel informationin a storage device; and wherein said authenticating step furtherincludes retrieving over a network said blood vessel information fromthe storage device.
 15. The apparatus according to claim 8, wherein thewavelength is 805 nm.
 16. The apparatus according to claim 9, whereinthe wavelength is one of 660 nm and 940 nm.